In the years that Watts Bar 2 lay fallow, policymakers and climate strategists have struggled to figure out what the future of renewable energy will look like. They have three options: find a way of cleaning up coal, build batteries capable of storing energy from capricious renewables, or go nuclear. Each has benefits and drawbacks. But nuclear is a strong contender because it is the only technology that actually exists. The Watts Bar reactors will provide power to 1.5 million households, and their only greenhouse gas emissions will come from the cars employees use to commute.

That’s a good deal, but still. Show a crowd a pair of cooling towers, and at least some of them will see an atomic apocalypse featuring three-eyed fish, leafless forests, and hospital-gowned Soviet defectors with skin like glistening mayonnaise. Nuclear power may be clean, but people still question whether it is, or ever will be, safe enough.

Those fears may be moot. Safety concerns didn’t delay construction on Watts Bar Unit 2 for so many years. Economics did. For all that fear, nuclear power still has the safest track record of any power source.

The Danger

Nuclear energy sources are dangerous because they emit radiation—particles and energy shed from unstable molecules trying to calm down. “Those radioactive missiles can hit the human body and damage cells or DNA,” says David Lochbaum, director of the Union of Concerned Scientist’s nuclear safety project. Enough radiation will give you cancer, or possibly even pass genetic mutations on to your kids. Too much can kill you outright.

But plants like Watts Bar don’t release much radiation into the environment. Inside, radioactive material heats water, which turns into steam, which spins the enormous turbines that generate electricity. Plants regularly release some of that water and steam at rates prescribed by the US Nuclear Regulatory Commission, and if you live downriver or downwind of one, the radiation within will raise your chances of developing a tumor by just one tenth of one percent. You’re far more likely to grow a tumor because you sneak a cigarette now and again.

But you aren’t afraid of routine releases. You’re terrified of another Three Mile Island, Fukushima, or Chernobyl.

These disasters were the result of a meltdown, which occurs when something impedes a reactor’s ability to cool the fuel. The US, where nearly 20 percent of electricity comes from 99 nuclear plants, uses uranium. Older reactors—which is every reactor in the US, including Watts Bar Unit 2—use electric pumps to move water through the system. The Fukushima disaster showed what happens it you have pumps but no power to use them. Newer generations rely on gravity instead, draining cooling water from elevated storage tanks to send it through the reactor core.

Those updates mean serious nuclear accidents are becoming ever more rare. Since Three Mile Island in 1979, the Nuclear Regulatory Commission found that the rate of shut-down-the-reactor-level problems has dropped from 2.5 per plant per year to around 0.1 (One such happened on March 29 in Washington). Even Three Mile Island wasn’t the disaster it could have been, because of that plant’s layers of redundant protection.

In terms of full blown nuclear disaster, there is really only one data point: Chernobyl. Which was horrifying. But in terms of real risk? The World Health Organization estimates the disaster will claim 4,000 lives, a figure that includes everything from direct victims to people born with genetic mutations well after the meltdown in 1986. By comparison, particulate matter from coal power plants kills about 7,500 people in the US every year. Radiation is the shark attack of environmental danger: An awful way to go, but far less likely than, say, a car wreck.

Spent fuel—about a third of the uranium in a reactor’s core is replaced every two years—is a bigger concern, because the US nuclear industry doesn’t have anywhere to dispose of it. Used rods sit in cooling tanks for five years, until they’re cold enough to encase in dry casks. But that fuel isn’t harmful unless you fall into the water (hello super powers! Actually, probably just radiation poisoning). Or the plumbing fails. Spent rods stashed away in dry casks are even less worrisome, because the containers would need to be breached enough to let air get in and cause a combustion.

这可能是核能的最大冒险因素：建造核能之后，要花太长的时间才能见到投资的收效，如果有收效的话<if one comes at all. >。假设你今天开始建造一座核电站。如果，在接下来的20年内的某个时刻，一群努力工作的天才发明了能够(良好)储存风电或者太阳能的电池，将煤炭造成的碳排放消除，或者（因不再需要开采而）解决了天然气的甲烷排放，那么你将核电站建好之后，你那昂贵的核能想在市场上占据一席之地的可能性非常渺茫。